DIELS-ALDER REACTION OF (1-METHYLENE-2-PROPENYL)COBALOXIME, 1-METHYLENE-2-PROPENYL-BIS(DIMETHYLGLYOXIMATO)PYRIDINE-COBALT(III)

(1-Methylene-2-propenyl)cobaloxime (1), a diene having a transition metal substituent, was prepared conveniently from 2-chloromagnesio-1,3-butadiene and chlorocobaloxime. Cobaloxime 1 gives Diels-Alder adducts with olefinic dienophiles (maleic anhydride, N-phenylmaleimide, p-benzoquinone, dimethyl fumarate, methyl vinyl ketone, and methyl acrylate) and acetylenic dienophiles (methyl propiolate and dimethyl acetylenedicarboxylate). The reactivity of cobaloxime 1 is higher than that of its metalloid analogs, such as 2-silyl-, 2-seleno-, and 2-stannyl-1,3-butadiene, though the reaction pattern is essentially the same. This additional activation of the diene system by cobaloxime is accounted for by a back donation of the filled d-orbital of cobalt(III) to the pi-system of the diene.